Encrypting files with AES in R

# visit http://reakkt.com for more information

### Encrypt/Decrypt a file using AES-256 ECB

# encryption key is SHA256 from the keyphrase
# before encryption file is compressed in-memory

### script parameters:

# key             - keyphrase
# input.file      - file to encrypt
# encrypted.file  - name of the encrypted output file
# decrypted.file  - name of the decrypted output file
# encrypt         - flag: encrypt (TRUE) or decrypt (FALSE)

key             <- "ala ma kota"

input.file      <- "enc.R"
encrypted.file  <- "test.enc"
decrypted.file  <- "test.R"

encrypt         <- FALSE

###

library(digest)
library(fBasics) # hex to dec conversion

### initialize AES

h   <- digest(key, algo="sha256", raw=TRUE)

aes <- AES(h, mode="ECB")

###

ReadClrFile <- function(file.name) {

  file.size    <- file.info(file.name)$size

  if (file.size>2147483647) error("ERROR: too large file.") # .Machine$integer.max

  file.obj     <- file(file.name,"rb")

  file.content <- readBin(con=file.obj,what=raw(),n=file.size)

  close(file.obj)

  return(file.content)

}

ReadEncFile <- function(file.name) {

  file.size    <- file.info(file.name)$size

  file.obj     <- file(file.name,"rb")

  file.content <- readBin(con=file.obj,what=raw(),n=file.size)

  close(file.obj)

  return( file.content )

}


SaveFile <- function(x,file.name) {

  file.obj     <- file(file.name,"wb")

  writeBin(x,con=file.obj)

  close(file.obj)

}

pad0 <- function(x,n=17) {

  l <- nchar(x)

  if (l<n) x <- paste(x,paste(rep("0",n-l),collapse=""),sep="")

  return(x)

}

AddGarbage16  <- function(x) {

  l <- length(x)

  if (l %% 16 !=0) {

    g  <- 16-(l %% 16)

    xg <- sapply(round(runif(g,0,255)), function(x) packBits(intToBits(x))[1])

    return( c(x,xg) )

  }

  return( x )

}

EncryptFile <- function(x) {

  xc <- memCompress(x,type="gzip")

  l  <- length(xc)

  h  <- charToRaw(pad0(.dec.to.hex(l)))

  xg <- AddGarbage16(xc)

  xe <- aes$encrypt(xg)

  return( c(h,xe) )

}

DecryptFile <- function(x) {

  fs    <- ExtractFileSize(x)

  xc    <- tail(x,-17)

  xc    <- head(aes$decrypt(xc,raw=TRUE),fs)

  x.clr <- memDecompress(xc,type="gzip")

  x.clr

}

# 2014-02-15: modified
ExtractFileSize <- function(x) {
    h0 <- head(x,17)

    # last character other than 30 ('0')
    idx <- tail(which(h0!=as.raw(0x30)),1)

    .hex.to.dec(rawToChar(h0[1:idx]))
}

###

if (encrypt) {

  x.clr  <- ReadClrFile(input.file)

  x.enc  <- EncryptFile(x.clr)

  SaveFile(x.enc,encrypted.file)

} else {

  x.enc <- ReadEncFile(encrypted.file)

  x.clr <- DecryptFile(x.enc)

  tmp   <- ReadClrFile(input.file)
  print(all.equal(x.clr,tmp))

  SaveFile(x.clr,decrypted.file)

}